Coherent anti-Stokes Raman spectroscopy (CARS) was used to obtain Raman spectra of thirteen polycyclic aromatic hydrocarbons (PAHs) composed of between three and seven fused rings. The compounds were pumped in the resonance and preresonance regions to obtain the sensitivity necessary for examination at concentrations down to 1.5 × 10 −5 M. A simple mixture of three PAHs was optically separated through the wavelength selectivity of the resonant enhancement process. Comparisons between the spectra of the mixture and the spectrum of each pure component showed essentially no differences when pumped at the same wavelength. Finally, lineshape analysis was performed on the CARS spectra to facilitate comparisons between classes of compounds and for quantitative purposes.
Three commercial oil samples were analyzed with the use of the selectivity of resonance CARS. No fractionation procedures were used; the oil samples were simply dissolved in an appropriate solvent and pumped from 365 nm to 480 nm. All three samples could be differentiated by characteristic Raman bands at various pump wavelengths. In addition, comparisons between the CARS spectra of the oil samples and the CARS spectra of pure PAHs at the same pump wavelength yielded tentative identifications of perylene and benzo(ghi)perylene in two of the samples.
The separation function for use In the optimization of complex separations relates the Information content of a chromatogram to the number and the extent of resolution between adjacent peaks. Each fully resolved peak Is arbitrarily assigned 2.0 bits of Information while partially resolved peaks are assigned 1 to 2 bits depending upon the depth of the valley between them. Pairs that give no valley but are detectable using a second-derivative method are assigned 0.5 bit. No a priori Information Is needed so the separation function may be easily Incorporated Into existing optimization schemes.Recently, the optimization of chromatographic separations has moved away from conventional methods in which a chromatographer uses experience and intuition to judge the
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